The present invention relates generally to optical modulating, splitting and recording, and more particularly to methods and associated apparatus for producing optical interference patterns and interferometric recordings from light modulated with a desired signal, data or information. As hereinafter used, the term "light" shall be understood to mean all electromagnetic radiation in the light portion of the spectrum, including visible, infrared and ultraviolet light.
In many interferometric recording applications, such as holographically produced images, two coherent light beams--an object beam which is modulated with information or a signal to be recorded and a reference beam which is not modulated--are both projected at a predetermined point so as to interfere optically thereat. A photosensitive medium is located at the predetermined point for recording the resultant interference pattern, thereby forming a holographic recording or filter. The holographic recording may thereafter be reproduced by directing a reproducing beam at the filter.
Although such holographic recording devices have proved adequate for some applications, certain disadvantages arise, especially where the recording medium is mounted to apparatus, such as a moving vehicle, which is subject to vibrations. In such applications, the independently produced object and reference beams may not impinge at their corresponding points on the photosensitive medium, thereby generating an image which may not be clear. In addition, with conventional interferometric or holographic recording techniques, it is impossible to obtain a "real time" recording, especially when applied to sophisticated detection systems such as systems for identifying radio frequency signals.
It is therefore an object of the present invention to provide a new and improved method and associated apparatus for providing a pair of light beams derived from the same signal beam for optically interfering together. Another object of the present invention is to provide a new and improved method and apparatus for recording the optical interference pattern between two interfering beams. It is another object of the present invention to provide a new and improved method and apparatus for recording the optical interference pattern between two interfering beams which are derived from a single signal-carrying beam.
It is also an object of the present invention to provide a new and improved method and associated apparatus for recording the optical interference pattern between two light beams, which is substantially insensitive to mechanical vibrations.
It is a further object of the present invention to provide a new and improved method and apparatus for recording the optical interference between two light beams, which permits real time recording of the resultant interference pattern.
It is still another object of the present invention to provide a new and improved method and apparatus for recording the optical interference between two light beams, enabling the use of a limited coherence light source.
It is yet another object of the present invention to provide a new and improved method and apparatus for recording the optical interference between two light beams and identifying therefrom signals such as radio frequency signals and other electromagnetic radiation.
Objects and advantages of the invention are set forth in part herein and in part will be appreciated herefrom, or may be learned by practice with the invention, the same being realized and attained by means of the methods, steps, operations, instrumentalities, structures and combinations pointed out in the appended claims. Accordingly, the invention consists in the novel methods, structures, combinations and improvements herein shown and described.